# Claude Mermaid MCP Server

MCP server for rendering Mermaid diagrams in Claude Code with **live reload** functionality and a built-in skill for expert guidance.

Automatically renders diagrams in your browser with real-time updates as you refine them. Perfect for iterative diagram development and documentation workflows.

![Demo](https://raw.githubusercontent.com/veelenga/claude-mermaid/main/assets/demo.gif)

## ✨ Features

- 🔄 **Live Reload** - Diagrams auto-refresh in your browser as you edit
- 🎨 **Multiple Save Formats** - Export to SVG, PNG, or PDF
- 🌈 **Themes** - Choose from default, forest, dark, or neutral themes
- 📐 **Customizable** - Control dimensions, scale, and background colors
- 🪄 **Interactive Preview** - Pan diagrams by dragging, zoom with browser controls, reset position with one click
- ⬇️ **Browser Export** - Download diagrams as SVG or PNG directly from the preview
- 🗂️ **Multiple Previews** - Use `preview_id` to work on multiple diagrams simultaneously
- 💾 **Persistent Working Files** - Live previews are stored under `~/.config/claude-mermaid/live`
- 🤖 **Built-in Skill** - Includes a Claude skill with best practices and expert guidance for creating diagrams

## Architecture

<details>
<summary>Project Architecture Diagram</summary>

![Architecture Diagram](https://raw.githubusercontent.com/veelenga/claude-mermaid/main/assets/architecture.png)

</details>

<details>
<summary>User Workflow Diagram</summary>

![User Workflow Diagram](https://raw.githubusercontent.com/veelenga/claude-mermaid/main/assets/workflow.png)

</details>

<details>
<summary>Dependencies Diagram</summary>

![Dependencies Diagram](https://raw.githubusercontent.com/veelenga/claude-mermaid/main/assets/dependencies.png)

</details>

## 🚀 Quick Start

### 1. Install

**Plugin Install (Recommended)**

In Claude Code, add the marketplace and install the plugin:

```bash
/plugin marketplace add veelenga/claude-mermaid
/plugin install claude-mermaid@claude-mermaid
```

Then restart Claude Code to activate the plugin.

**From npm:**

```bash
npm install -g claude-mermaid
```

**From source:**

```bash
git clone https://github.com/veelenga/claude-mermaid.git
cd claude-mermaid
npm install && npm run build && npm install -g .
```

### 2. Verify Installation

**Plugin install:** The MCP server is configured automatically. Just verify:

```bash
/mcp
```

You should see `mermaid` in the MCP server list.

**npm install:** Configure the MCP server manually:

```bash
claude mcp add --scope user mermaid claude-mermaid
```

Then verify:

```bash
claude mcp list
```

You should see `mermaid: claude-mermaid - ✓ Connected`

## 🔌 Other MCP Client Configurations

While this server is optimized for Claude Code, it can work with any MCP-compatible client. Here's how to configure it for other popular tools:

<details>
<summary><strong>Codex</strong></summary>

Add to your Codex MCP settings file (`~/.codex/mcp_settings.json`):

```json
{
  "mcpServers": {
    "mermaid": {
      "command": "claude-mermaid"
    }
  }
}
```

Or configure via Codex CLI:

```bash
codex mcp add mermaid claude-mermaid
```

</details>

<details>
<summary><strong>Cursor</strong></summary>

Add to your Cursor MCP config file (`.cursor/mcp.json` or settings):

```json
{
  "mcpServers": {
    "mermaid": {
      "command": "claude-mermaid"
    }
  }
}
```

Or use Cursor's settings UI:

1. Open Cursor Settings (Cmd/Ctrl + ,)
2. Navigate to MCP Servers
3. Add a new server with command: `claude-mermaid`

</details>

<details>
<summary><strong>VSCode with Cline Extension</strong></summary>

If using the [Cline extension](https://github.com/cline/cline) for VSCode:

1. Open VSCode settings (Cmd/Ctrl + ,)
2. Search for "Cline MCP"
3. Add to MCP Settings JSON:

```json
{
  "mcpServers": {
    "mermaid": {
      "command": "claude-mermaid"
    }
  }
}
```

</details>

<details>
<summary><strong>Windsurf</strong></summary>

Add to Windsurf's MCP configuration file:

```json
{
  "mcpServers": {
    "mermaid": {
      "command": "claude-mermaid"
    }
  }
}
```

Configuration location varies by platform:

- **macOS:** `~/Library/Application Support/Windsurf/mcp.json`
- **Linux:** `~/.config/windsurf/mcp.json`
- **Windows:** `%APPDATA%\Windsurf\mcp.json`

</details>

<details>
<summary><strong>Gemini CLI</strong></summary>

Add to Gemini CLI's MCP configuration file (`~/.gemini/mcp.json`):

```json
{
  "mcpServers": {
    "mermaid": {
      "command": "claude-mermaid"
    }
  }
}
```

Or use the Gemini CLI to configure:

```bash
gemini config mcp add mermaid --command claude-mermaid
```

</details>

<details>
<summary><strong>Other MCP Clients</strong></summary>

For any MCP-compatible client, use the standard configuration:

```json
{
  "mcpServers": {
    "mermaid": {
      "command": "claude-mermaid"
    }
  }
}
```

The command `claude-mermaid` should be available in your PATH after installation.

**Note:** Some clients may require the full path to the executable:

- Find the path: `which claude-mermaid` (Unix/macOS) or `where claude-mermaid` (Windows)
- Use absolute path in config: `"command": "/path/to/claude-mermaid"`

</details>

## 💡 Usage

Simply ask Claude Code to create Mermaid diagrams naturally. When installed as a plugin, the built-in `mermaid-diagrams` skill provides expert guidance, best practices, and automatic workflow management.

### Basic Examples

```
"Create a Mermaid diagram showing the user authentication flow"
"Draw a sequence diagram for the payment process"
"Generate a flowchart for the deployment pipeline"
```

### Advanced Examples

**With custom formatting:**

```
"Create a dark theme architecture diagram with transparent background"
"Generate a forest theme flowchart and save to ./docs/flow.svg"
```

**With specific output format:**

```
"Create an ER diagram and save as PDF to ./docs/schema.pdf"
"Save the flowchart as PNG to ./docs/flow.png"
```

_Note: Browser always shows SVG for live preview, while saving to your chosen format._

**Iterative refinement:**

```
"Create a class diagram for the User module"
// Browser opens with live preview
"Add the Address and Order classes with relationships"
// Diagram updates automatically in browser!
```

### Complete Example

```
"Create a flowchart and save to ./docs/auth-flow.svg:

graph LR
    A[User Login] --> B{Valid Credentials?}
    B -->|Yes| C[Access Granted]
    B -->|No| D[Access Denied]
    C --> E[Dashboard]
    D --> F[Try Again]

    style A fill:#e1f5ff
    style C fill:#d4edda
    style D fill:#f8d7da
"
```

The diagram will be saved to `./docs/auth-flow.svg` and opened in your browser with live reload enabled.

## 🔧 Tools and Parameters

There are two tools exposed by the MCP server:

1. `mermaid_preview` — render and open a live preview

- `diagram` (string, required) — Mermaid diagram code
- `preview_id` (string, required) — Identifier for this preview session. Use different IDs for multiple concurrent diagrams (e.g., `architecture`, `flow`).
- `format` (string, default `svg`) — One of `svg`, `png`, `pdf`. Live preview is available only for `svg`.
- `theme` (string, default `default`) — One of `default`, `forest`, `dark`, `neutral`.
- `background` (string, default `white`) — Background color. Examples: `transparent`, `white`, `#F0F0F0`.
- `width` (number, default `800`) — Diagram width in pixels.
- `height` (number, default `600`) — Diagram height in pixels.
- `scale` (number, default `2`) — Scale factor for higher quality output.

2. `mermaid_save` — save the current live diagram to a path

- `save_path` (string, required) — Destination path (e.g., `./docs/diagram.svg`).
- `preview_id` (string, required) — Must match the `preview_id` used in `mermaid_preview`.
- `format` (string, default `svg`) — One of `svg`, `png`, `pdf`. If the live working file for this format doesn’t exist yet, it is rendered on demand before saving.

## 🎯 How Live Reload Works

1. **First render:** Opens diagram in browser at `http://localhost:3737/{preview_id}`
2. **Make changes:** Edit the diagram through Claude Code
3. **Auto-refresh:** Browser detects changes via WebSocket and reloads
4. **Status indicator:** Green dot = connected, Red dot = reconnecting

The live server uses ports 3737-3747 and automatically finds an available port.

### Live Preview Controls

- **Pan:** Click and drag the diagram to move it around
- **Zoom:** Use browser zoom (Ctrl/Cmd + +/- or pinch-to-zoom on trackpad)
- **Reset Position:** Click the ⊙ button in the status bar to recenter the diagram
- **Export:** Click the ⬇ button to download as SVG or PNG

### Notes

- Live preview is available for `svg` format only; PNG/PDF are rendered without live reload.
- For sequence diagrams, Mermaid does not support `style` directives inside `sequenceDiagram`.

## 🖥️ Standalone server

You can start the preview server without an AI agent using the `--serve` flag:

```bash
claude-mermaid --serve
```

This opens the diagram gallery in your browser with all previously rendered diagrams. Useful for browsing and exporting diagrams outside of a Claude Code session.

## 🛠️ Development

```bash
# Install dependencies
npm install

# Build the project
npm run build

# Run tests
npm test

# Watch mode for development
npm run dev

# Start the MCP server directly
npm start
```

## 📝 Troubleshooting

**Error: Cannot find package 'puppeteer':**

This is a rare environment-specific issue. Try these solutions:

1. **Install claude-mermaid globally**:

   ```bash
   npm install -g claude-mermaid
   ```

2. **Reinstall the plugin** in Claude Code:
   ```
   /plugin uninstall claude-mermaid
   /plugin install claude-mermaid@claude-mermaid
   ```

**Server not connecting:**

```bash
# Check if server is installed
claude-mermaid -v

# Reinstall if needed
npm install -g claude-mermaid

# Verify MCP configuration
claude mcp list
```

**Permission denied error:**

```bash
# Make sure the binary is executable
chmod +x $(which claude-mermaid)
```

**Port already in use:**

- The server uses ports 3737-3747
- It will automatically find an available port
- Check if another process is using these ports: `lsof -i :3737-3747`

**Diagrams not rendering or live reload not working:**

The server logs to `~/.config/claude-mermaid/logs/`:

- `mcp.log` - Tool requests and diagram rendering
- `web.log` - HTTP/WebSocket connections and live reload

Enable debug logging in your MCP config:

```json
{
  "mcpServers": {
    "mermaid": {
      "command": "claude-mermaid",
      "env": {
        "CLAUDE_MERMAID_LOG_LEVEL": "DEBUG"
      }
    }
  }
}
```

Then check the logs:

```bash
# View MCP operations
tail -f ~/.config/claude-mermaid/logs/mcp.log

# View WebSocket connections
tail -f ~/.config/claude-mermaid/logs/web.log
```

Available log levels: `DEBUG`, `INFO` (default), `WARN`, `ERROR`, `OFF`

## 🤝 Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

## 📄 License

MIT - see [LICENSE](LICENSE) file for details

## 🔗 Links

- [GitHub Repository](https://github.com/veelenga/claude-mermaid)
- [npm Package](https://www.npmjs.com/package/claude-mermaid)
- [Claude Code Documentation](https://docs.claude.com/claude-code)
- [Mermaid Documentation](https://mermaid.js.org/)

## 👀 See Also

If you like this project, you might also be interested in

- [preview-skills](https://github.com/veelenga/preview-skills) — preview skills for visualizing files in the browser (markdown, csv, json, mermaid and more)

## Hosted deployment

A hosted deployment is available on [Fronteir AI](https://fronteir.ai/mcp/veelenga-claude-mermaid).